The present invention relates generally to telemetry transceivers associated with active implantable medical devices (AIMDs) and related components. More particularly, the present invention relates to AIMD RF telemetry circuits having radio frequency identification (RFID) controllable wake-up features.
FIGS. 1 and 2 provide a background for better understanding of the present invention. FIG. I is a wire formed diagram of a generic human body showing a number of implanted medical devices. 100A represents a family of hearing devices which can include the group of cochlear implants, piezoelectric sound bridge transducers and the like. 100B represents a variety of neurostimulators and brain stimulators. Neurostimulators are used to stimulate the Vagus nerve, for example, to treat epilepsy, obesity and depression. Brain stimulators are pacemaker-like devices and include electrodes implanted deep into the brain for sensing the onset of the seizure and also providing electrical stimulation to brain tissue to prevent the seizure from actually occurring. The lead wires associated with a deep brain stimulator are often placed using real time MRI imaging. 100C shows a cardiac pacemaker which is well-known in the art. 100D includes the family of left ventricular assist devices (LVAD's) and artificial hearts. 100E includes an entire family of drug pumps which can be used for dispensing of insulin, chemotherapy drugs, pain medications and the like. Insulin pumps are evolving from passive devices to ones that have sensors and closed loop systems. That is, real time monitoring of blood sugar levels will occur. These devices tend to be more sensitive to EMI than passive pumps that have no sense circuitry or externally implanted lead wires. 100F includes a variety of bone growth stimulators for rapid healing of fractures. 100G includes urinary incontinence devices. 100H includes the family of pain relief spinal cord stimulators and anti-tremor stimulators. 100H also includes an entire family of other types of neurostimulators used to block pain. 100I includes a family of implantable cardioverter defibrillators (ICD) devices and also includes the family of congestive heart failure devices (CHF). This is also known in the art as cardio resynchronization therapy devices, otherwise known as CRT devices. 100J illustrates an externally worn pack. This pack could be an external insulin pump, an external drug pump, an external neurostimulator or even a ventricular assist device.
FIG. 2 is a prior art cardiac pacemaker 100C. A cardiac pacemaker typically has an electromagnetically shielded and hermetically sealed housing 102 which is generally constructed from titanium, stainless steel or the like. It also has a plastic or Techothane header block 104 which houses ISO standard IS-1 type connectors 106, 108. In the past, AIMDs, in particular pacemakers, ICDs and neurostimulators, embodied close-coupled telemetry circuits. The purpose of telemetry is so that the AIMD could be interrogated or even reprogrammed after implantation. For example, it is common to monitor battery status, patient biologic conditions and the like, through telemetry. In addition, an external telemetry programmer can be used to re-program the AIMD, for example, and put it into different modes of operation. In the past, for pacemakers and ICDs the telemetry was inductive (low frequency magnetic) and close coupled. In this older art it was typical that the AIMD would have a multiple turn wire antenna within its titanium housing. There were even AIMDs that used an external loop antenna of this type. To interrogate or re-program the AIMD, the physician or other medical practitioners would bring a wand, with a similar antenna embedded in it, very close to the AIMD. For example, for a typical pacemaker application the telemetry wand would be placed directly over the implant. The wand is/was connected with wiring to the external programmer. The medical practitioner would move the wand around until the “sweet-spot” was located. Once the wand is located in the “sweet-spot,” a communication link is established between the multiple turn wire antenna implanted in the AIMD and a similar multiple turn wire antenna located inside the telemetry wand. The external programmer would then become active and electrograms and other important information would be displayed. Typically the telemetry wand would be placed either against or very close to the patient's skin surface or at most a few centimeters away.
In the last few years, distance RF telemetry has become increasingly common. For distance telemetry, for example for a cardiac pacemaker 100C, there would be a high frequency antenna that would be located outside of the AIMD shielded titanium housing 102. This could, for example, be placed in or adjacent to the AIMD plastic header block 104. The external antenna would communicate with an external programmer that would have its own RF transceiver. A typical band for such communication is in the 402 to 405 MHz frequency range (known as the MICS band). There are other bands that may be used for RF telemetry including gigahertz frequencies. A problem with such prior art RF distance telemetry circuits is that energy consumption is high because the receiver circuitry must be on all the time.
The Zarlink chip has provided one solution to this problem. The Zarlink chip uses higher frequencies (in the gigahertz range) to wake-up the lower frequency RF telemetry circuit which is generally in the MICS band. The higher frequency GHz receiver of the Zarlink chip is very energy efficient, however the device or chip still consumes an amount of idling energy from the AIMD battery to always be alert for its wake-up call. In general, this current draw link is in the order of 250 picoamperes (250,000 nanoamperes). This is still a significant amount of idling current over the life of the pacemaker and generally shortens the pacemaker life by at least one month.
Accordingly, there is a need for an RF activated AIMD telemetry transceiver that includes means responsive to a signal from an RF transmitter to place an AIMD telemetry transceiver into its active telemetry mode. During a sleep mode for the AIMD telemetry transceiver, the system should draw a minimal amount of power from the AIMD, on the order of 25,000 nanoamperes or less, and preferably 500 nanoamperes or less. A circuit connection is provided which would be responsive to a signal from the RF tag to place the telemetry transceiver into its active telemetry mode. Preferably, the entire wake-up feature would be externally powered by, for example, the energy coupled from an external/remote RF reader. Once the AIMD telemetry transceiver is placed into its active mode, a feature is needed wherein the AIMD telemetry circuit can go back into its quiescent sleep mode. Accordingly, there is need for circuits and/or programmer commands to place the AIMD telemetry receiver back into a sleep mode after a set amount of time or after a receipt of a signal from the external programmer. The present invention fulfills these needs and provides other related advantages.